The ultimate goal of this project is to determine whether cultured lymphocytes represent a superior model for studying in vitro senescence. Since the aging immune system has been postulated as one of the causes of biological aging, lymphocytes are an eminently suitable, yet heretofore unexplored, model for studying senescence in vitro. T cell cultures and clones will be established from normal newborn and adult lymphocytes, and will be analyzed for growth, functional and cell surface characteristics. Any clones which show unlimited growth, with no signs of senescence, will be examined for signs of transformation. Thus, the biological question of whether normal lymphocytes conform to the Hayflick limit will be addressed.